1. Field of the Invention
This invention relates to a rotation angle detector used for detecting the rotation angle of the steering wheel of automobiles, etc.
2. Description of the Related Art
As a rotation angle detector, there is, for instance, a steering wheel rotation angle detector that is interlocked with the steering wheel of an automobile for the automatic control of its headlamp irradiation direction so that it may change leftward and rightward. Such measurement of the wheel rotation angle must be capable of measuring a rotation angle of the steering shaft beyond 360xc2x0 since the steering wheel can turn several times left or right every time.
As such a steering wheel rotation angle detector, the applicant has proposed in Published Patent Application No. 2000-009822 a rotation angle detector in which an MR sensor is disposed in the vicinity of a rotating member rotating in conjunction with the steering shaft in order to detect the periodical angle position of said rotating member and a CPU makes the operation/processing of the data from said MR sensor, using the standard angle position stored in a non-volatile data memory, to calculate an absolute steering angle, including the indication of how many times the steering wheel has turned. Since no steering wheel angle data is used when the ignition switch is off, this device is operated intermittently during the period when said switch is off to enable tracing the current wheel angle position and also saving power consumption for the CPU operation.
In the above device, its intermittent operation while the ignition switch is off can effectively save the power consumption, but if batteries are left uncharged for many hours, it may nevertheless considerably reduce the remaining power therein.
An object of this invention is therefore to provide a rotation angle detector that has been improved so as to remarkably reduce power consumption when the detector is at rest and uses no detection data.
Therefore, a first aspect according to the invention is provided with a rotating member rotating in conjunction with a body of rotation to be measured, an angle sensor disposed in the vicinity of the rotating members to detect their periodical angle positions, a non-volatile data memory for storing the standard position of the angle sensor, an operation/control means that performs the operation/processing of the standard position and the detection data from the angle sensor to determine the periodicity of the rotating member, calculates an absolute rotation angle of the body of rotation to be measured to provide a detection output, and when a stop signal is received from outside, changes from a normal operation mode of continuously reading detection data from the angle sensors and performing the operation/processing thereof to a stop mode of suspending the operation/processing, and a rotation detection means to detect that the rotating member have rotated to a prescribed angle position during the stop mode;
the operation/control means causing to store the values of angle position and periodicity of the rotating member at the time point when the stop mode is switched to, releasing the stop mode by an output signal received from the rotation detection means, determining a value to correct the periodicity of the rotating member based on the change of angle position of the rotating member taking place during a period from the start of the stop mode to its release and using this value for correction.
Upon receiving a stop signal, the operation/control means switches to the stop mode of suspending its operation/processing, so its power consumption can be saved during the stop mode. If the rotating member has rotated to a prescribed angle position during the stop mode, the operation/control means temporarily releases the stop mode, judges whether the rotating member has exceeded the standard position, based on its angle positional change, and if so, corrects its periodicity, so the current periodicity can always be known even when the operation/control means is at rest.
A second aspect according to the invention is that a comparator that receives the output signal from the angle sensor is used as the rotation detection means.
By using a comparator as the rotation detection means, whether the rotating members have rotated to a prescribed angle position can easily be judged based on the comparator output conditions.
A third aspect according to the invention is that a hysteresis has been set up in the output from the comparator.
Setting up a hysteresis in the output from the comparator can facilitate the comparator to stably detect that the rotating member has rotated.
A fourth aspect according to the invention is that power voltage supplied to the angle sensors is set up at a low level during the stop mode.
A low-level power voltage supplied to the angle sensor during the stop mode can further save power consumption.